Moody's Investors Service downgraded another $16.7 billion of securities backed by subprime residential mortgages Thursday as the loans' performance continues to worsen.

The rating agency has downgraded hundreds of billions of dollars worth of residential mortgage-backed securities in recent months as credit raters have steadily increased loss expectations on them because of low home prices, high unemployment and a slow recovery.

On Thursday Moody's downgraded 251 tranches from 52 residential mortgage-backed transactions issued by Morgan Stanley from 2005 to 2007. It upgraded five tranches.

Subscribe Now

Access to authoritative analysis and perspective and our data-driven report series.

14-Day Free Trial

No credit card required. Complete access to articles, breaking news and industry data.